The present invention is directed to a door for a single-face station of a machine that produces corrugated cardboard and, particularly, to a rear door which is fitted on rails and closes an inner volume of the single-face station in such a way that the volume can be placed under pneumatic pressure.
Usually, a single-face station is located upstream of the machine that produces the cardboard. A first web is corrugated, when it travels between two corrugating rolls of the single-face station, and then receives glue on the crest of the flutes of the corrugations while the corrugated sheet is on the lower of the two corrugating rollers from a gluing unit. Then, a second covering sheet is applied by a third lower pressure roll onto the crest of the flutes that have been provided with glue.
The frame of such a station comprises a stand with two lateral walls, whose front edges support the two corrugating rolls and the lower pressure roll, which make up, in a certain way, a front wall. The gluing unit, whose front glue-applying roll is brought at a very precise distance close to the rear lower part of the second lower corrugating roll, is located between the two lateral walls. This gluing unit is usually mounted on rails in order to be taken out from the back of the station for cleaning, maintenance and repair, as well as to allow an easy access to the rolls from the back for similar operations.
A recent technique for keeping the corrugating web perfectly applied against the flutes of the rear part of the second corrugating roll where the gluing operation takes place consists in closing the upper part of the station by means of a plate, as well as a rear side by means of a door, and to pressurize the inner volume thus defined with a pneumatic pressure of, say, 50 to 60 millibars. Obviously, this door is to be reopened for the gluing unit to be taken out, if necessary, which fact causes the double problem of interlocking and sealing of the door.
A rear door of a single face station is known to be fitted on a pair of rails for an orthogonal translation and, with analogy to the doors of a bank safe, has a first front part with dimensions slightly smaller than the openings of the framework and a rear rim with a larger dimension. The first part of this door is completed with a series of latches situated in a vertical plane and which are meant to penetrate into orifices machined in the inner section of the opening. The vertical front sides of the rear rim are provided with elastomer tightening seals which engage on the rear side of the framework of the opening. Thus, when the door is shut, it is necessary to first push it against the framework in order to squeeze the tightening seal and to bring the latches in correspondence with the openings prior to the turning of the handle in order to engage these latches. The shutting process is difficult for an operator, especially due to the use of mechanical devices for gearing down the actuation of the latches. In fact, the existence of the mechanical gearing-down device allows for disengagement of the latches, although an overpressure still exists in the inner volume. It is, therefore, necessary to foresee an auxiliary independent security device in order to prevent a manipulation error which is liable to create a dangerous situation for the operator, which is the pressure still in the inner volume.